Many real-world computer-implemented operations involve making changes in multiple computer systems. Such operations are referred to herein as “multi-system operations”. For example, the online purchase of an airline ticket may involve adjusting seat availability in an airline's database system, as well as adjusting account balance in one or more bank database systems. Since the changes made by multi-system operations are logically all part of the same high-level operation, it is preferable that either all of the changes be made permanent, or that none of the changes are made permanent. When only a subset of the changes required by a multi-system operation are made permanent, the systems are left in an inconsistent state (e.g. the customer is charged for an airline ticket, but no seat is reserved for the customer).
When the database systems that are involved in a multi-system operation are tightly coupled, inconsistent states can be avoided using a technique referred to as two-phase commit. In two-phase commit, all systems wait until all other systems are “prepared” to make their changes permanent (“commit”). At that point, all systems commit in unison. If any system cannot achieve the “prepared” state, then all systems “roll back” to remove all changes made relative to the multi-system operation.
While the two-phase commit protocol guarantees that a multi-system operation is treated as an atomic unit (either entirely commits, or entirely fails), it does so at the expense of performance. For example, when the systems involved in the multi-system operation are not tightly coupled, the inter-system interactions required by the two-phase commit protocol may impose unacceptable delays. Further, one or more of the systems involved in the multi-system operation may not support the two-phase commit protocol.
To avoid having resources locked while waiting for other systems involved in a two-phase commit operation, techniques have been developed for avoiding two-phase commit in multi-system operations. One such technique is described in U.S. Pat. No. 7,904,434 entitled “Framework for handling business transactions”. In the technique described therein, operational constraints set forth conditions that must be satisfied before an update is allowed to proceed. If an attempt is made to update a particular value that has changes that may be undone, then the database server determines a plurality of “possible result values” for the particular value. If the possible result values satisfy the operational constraint conditions, then the update is allowed to proceed.
Unfortunately, formulating such operation constraint conditions may not be straightforward or even possible for some types of multi-system operations. Further, it is possible that some systems involved in the multi-system operations do not support such operational constraints. Consequently, there is a need to perform multi-system operations in a way that does not impose the delays of two-phase commit, and that does not require the programming of operational constraint conditions.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.